1. Field of the Invention
The present invention relates to a cutting fluid filtering device used to remove a chip or sludge mixed in a cutting fluid in a machine tool.
2. Description of the Related Art
In a machine tool, impurities such as a chip and sludge generated during machining are mixed into a cutting fluid to adversely affect the performance and reliability of the machine tool, and hence a filter for removing the impurities is used. For the purpose of maintaining the purification performance and prolonging the life of the filter, the filter is washed. As a method for washing the filter, for example, as described in Japanese Patent Application Laid-open No. 2006-272474, Japanese Patent Application Laid-open No. 2006-255833, and Japanese Patent Application Laid-open No. 2001-252847, there are cases where backwashing in which the cutting fluid is flown in a direction reverse to the direction of flow of the cutting fluid during its normal use and the chip and sludge adhering to the filter are thereby removed is performed.
Herein, the outline of the backwashing will be described. First, inflow-side and outflow-side ducts of a container with a filter (filter container) subjected to the backwashing are closed such that the filter and the cutting fluid remaining in the filter container cannot move. Subsequently, by supplying compressed air into the filter in a direction reverse to the direction of flow of the cutting fluid during its normal use and opening a discharge valve of a discharge duct connected to the filter container, the cutting fluid pressurized by the supplied compressed air is caused to pass through the filter and flow into the opened discharge duct. By the flow of the cutting fluid, impurities adhering to the filter such as the chip and sludge are removed.
A description will be given of an example of a conventional cutting fluid filtering device of the machining tool by using FIG. 10.
The reference numeral 10 denotes a tank, the reference numeral 11 denotes a filter pump, the reference numeral 12 denotes a inflow-side valve, the reference numeral 13 denotes a filter container with a filter, the reference numeral 14 denotes a differential pressure switch, the reference numeral 15 denotes a discharge valve, the reference numeral 16 denotes an air source, the reference numeral 17 denotes an air supply valve, the reference numeral 18 denotes an outflow-side valve, the reference numeral 19 denotes a cutting fluid containing chips, and the reference numerals 20, 21, 22, and 23 denote ducts. The reference numeral 70 denotes a machine tool main body.
A cutting fluid filtering device 1 controlled by a controller (not shown) is caused to operate to drive the filter pump 11, the cutting fluid containing chips 19 is pumped up from the tank 10 through the duct 20 to be caused to pass through the filter container 13, and the cutting fluid filtered by the filter in the filter container 13 is supplied to the machining tool main body 70. The filter (not shown) for filtering out chips from the cutting fluid containing chips is attached in the filter container 13.
As the purification of the cutting fluid containing chips 19 stored in the tank 10 is continued, the amount of the chip adhering to the filter in the filter container 13 is gradually increased. As a result, a difference in pressure between the duct 21 on the side of inflow to the filter container 13 and the duct 22 on the side of outflow from the filter container 13 is gradually increased. When the pressure difference between the inflow-side duct 21 and the outflow-side duct 22 becomes not less than a preset pressure difference, the differential pressure switch 14 is activated and backwashing is started.
At the start of the backwashing, first, the drive of the filter pump 11 is stopped, the pumping of the cutting fluid containing chips 19 stored in the tank 10 is suspended, and the inflow-side duct 21 and the outflow-side duct 22 of the filter container 13 are closed using the inflow-side valve 12 and the outflow-side valve 18. With this, the cutting fluid remaining in the filter container 13 cannot flow out to the tank 10 or the machining tool main body 70.
Subsequently, the air supply valve 17 connected to the air source 16 is opened, and compressed air is supplied into the filter container 13 in a direction reverse to the direction of flow of the cutting fluid during its normal use. By closing the air supply valve 17 connected to the air source 16 and opening the discharge valve 15 connected to the filter container 13, the cutting fluid pressurized by the compressed air from the air source 16 is caused to pass through the filter in the filter container 13 in the direction reverse to the direction of flow of the cutting fluid during its normal use and return to the tank 10 through the duct 23. By the flow of the cutting fluid, the chip and sludge adhering to the filter are removed.
In the conventional art described above, a structure is adopted in which the differential pressure switch 14 attached to the filter from which the chip is to be removed is set so as to be activated when the predetermined pressure difference occurs, and the backwashing is performed with a signal from the differential pressure switch. Note that a pressure sensor can be used instead of the differential pressure switch 14.